Static magnetic devices such as transformers and inductors are essential elements in a wide variety of circuits requiring energy storage and conversion, impedance matching, filtering, EMI suppression, voltage and current transformation, and resonance. As historically constructed, these devices tended to be bulky, heavy and expensive to fabricate as compared with other circuit components. Manual operations such as winding conductive wire around magnetic cores dominated production costs.
A new approach to the fabrication of such devices was described in U.S. application Ser. No. 07/695653 entitled "Multilayer Monolithic Magnetic Components and Method of Making Same" filed by Grader et al and assigned to applicants' assignee. In the Grader et al approach ceramic powders are mixed with organic binders to form magnetic and insulating (non-magnetic) green ceramic tapes, respectively. A magnetic device is made by forming layers having suitable two-dimensional patterns of magnetic and insulating regions and stacking the layers to form a structure with well-defined magnetic and insulating non-magnetic regions. Conductors are printed on the insulating regions as needed, and the resulting structure is laminated under low pressure in the range 500-3000 psi at a temperature of 60.degree.-80.degree. C. The laminated structure is fired at a temperature between 800.degree. to 1400.degree. C. to form a co-fired composite structure of the magnetic component.
Using this approach, one must take particular care that the materials used be thermally compatible with one another. The magnetic and the insulating materials must have compatible sintering rates and temperatures. Such compatibility is achieved, for example, by doping the insulating material with metals.
If the materials are not highly compatible, they tend to crack during the sintering process. Even if they do not crack, the residual stresses may significantly degrade the magnetic characteristics of the device through magnetostriction. Accordingly, there is a need for a method for making multilayer magnetic components that is more tolerant of differences in the sintering and thermal expansion properties of the constituent ceramic materials.